Bluetooth priority issues

I just upgraded from an S4 to the S8. This was not an issue with the S4.

I have my phone paired to a Plantronics Bluetooth headset. It's also paired to my truck ('16 F150 with sync 3). Whenever i get in my truck, the truck takes over from the headset. With my S4 the truck didn't sync unless the headset wasn't paired to my phone (off or left it home).

How can I set this back up to the way it was before? Where all calls stay on my headset and I can listen to the radio in the truck, not have the phone connect to both

Welcome to the forums as a new member! Remove the pairing for the truck from the truck and phone. When you re-pair you should see the option for media, choose no for that one. There is also the possibly you'll need a firmware update for the truck to support the S8, depends on lots of things. You might ask your dealer if one is available.

More like you enjoyed a failing point in the S4's bluetooth setup that was corrected in later versions of samsungs bluetooth stack. In a normal scenario, connecting a NEW audio output device relays the intent that you wish to be using that device over the current device. If I am playing music over a speaker, I don't connect my headphones to it unless I explicitly intend to listen through my headphones. The fact that your truck auto reconnects everytime power is applied is simply your truck failing to offer an easy manual mode.

Also your truck is supporting you with a hands free bluetooth wireless mode for your calls, of which the only way you can usualy disable is by unpairing the phone. I find that on my mazda, telling it to not use the a2dp profile for music while keeping the hands free feature for calls is futile as well, seconds later it re-enables it.